Responsiveness and minimal clinically important difference for pain and disability instruments in low back pain patients

BMC Musculoskeletal Disorders BioMed Central Research article Open Access Responsiveness and minimal clinically important difference for pain and disability instruments in low back pain patients Henrik H Lauridsen*1, Jan Hartvigsen1,2, Claus Manniche1,3, Lars Korsholm1,4 and Niels Grunnet-Nilsson1 Address: 1Clinical Locomotion Science, Institute of Sports Science and Clinical Biomechanics, University of Southern Denmark, Odense, Denmark, 2Nordic Institute of Chiropractic and Clinical Biomechanics, Odense, Denmark, 3Backcenter Funen, Ringe, Denmark and 4Department of Statistics, University of Southern Denmark, Odense, Denmark Email: Henrik H Lauridsen* - ; Jan Hartvigsen - ; Claus Manniche - ; Lars Korsholm - ; Niels Grunnet-Nilsson - * Corresponding author Published: 25 October 2006 BMC Musculoskeletal Disorders 2006, 7:82 doi:10.1186/1471-2474-7-82 Received: 15 May 2006 Accepted: 25 October 2006 This article is available from: http://www.biomedcentral.com/1471-2474/7/82 © 2006 Lauridsen et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract Background: The choice of an evaluative instrument has been hampered by the lack of head-to-head comparisons of responsiveness and the minimal clinically important difference (MCID) in subpopulations of low back pain (LBP). The objective of this study was to concurrently compare responsiveness and MCID for commonly used pain scales and functional instruments in four subpopulations of LBP patients. Methods: The Danish versions of the Oswestry Disability Index (ODI), the 23-item Roland Morris Disability Questionnaire (RMQ), the physical function and bodily pain subscales of the SF36, the Low Back Pain Rating Scale (LBPRS) and a numerical rating scale for pain (0–10) were completed by 191 patients from the primary and secondary sectors of the Danish health care system. Clinical change was estimated using a 7-point transition question and a numeric rating scale for importance. Responsiveness was operationalised using standardardised response mean (SRM), area under the receiver operating characteristic curve (ROC), and cut-point analysis. Subpopulation analyses were carried out on primary and secondary sector patients with LBP only or leg pain +/- LBP. Results: RMQ was the most responsive instrument in primary and secondary sector patients with LBP only (SRM = 0.5–1.4; ROC = 0.75–0.94) whereas ODI and RMQ showed almost similar responsiveness in primary and secondary sector patients with leg pain (ODI: SRM = 0.4–0.9; ROC = 0.76–0.89; RMQ: SRM = 0.3–0.9; ROC = 0.72–0.88). In improved patients, the RMQ was more responsive in primary and secondary sector patients and LBP only patients (SRM = 1.3–1.7) while the RMQ and ODI were equally responsive in leg pain patients (SRM = 1.3 and 1.2 respectively). All pain measures demonstrated almost equal responsiveness. The MCID increased with increasing baseline score in primary sector and LBP only patients but was only marginally affected by patient entry point and pain location. The MCID of the percentage change score remained constant for the ODI (51%) and RMQ (38%) specifically and differed in the subpopulations. Conclusion: RMQ is suitable for measuring change in LBP only patients and both ODI and RMQ are suitable for leg pain patients irrespectively of patient entry point. The MCID is baseline score dependent but only in certain subpopulations. Relative change measured using the ODI and RMQ was not affected by baseline score when patients quantified an important improvement. Page 1 of 16 (page number not for citation purposes) BMC Musculoskeletal Disorders 2006, 7:82 Background As clinicians and researchers we often wish to address change in a patient's condition as a result of an intervention or to distinguish individual differences in response to treatment [1]. A prerequisite for this is measurement tools that accurately assess function and monitor change over time. Standardised self-report questionnaires provide such tools and are convenient for collecting large amounts of information on for instance pain and activity limitation. Apparently similar and well-validated back-specific questionnaires have emerged over the last decade making the choice of a proper instrument for a given situation challenging [2-5]. Criteria for instrument selection have often been based on whether a particular questionnaire is reliable and valid with respect to the patient population in question but this is changing. Many authors now advocate that the property of responsiveness, defined as the ability of an instrument to detect clinically relevant change over time, is equally or even more important in the choice of an evaluative instrument [6-11]. As a consequence, no less than 31 indices have been developed and reported in the literature making both the choice of an index and comparisons between indices confusing and difficult [12]. Several approaches to classifying clinically meaningful change (responsiveness) have been proposed based on study design and the construct of change being quantified [11-16]. One such approach is the differentiation between distribution-based and anchor-based methods, the former including those based on sample variability and measurement precision. The anchor-based methods, on the other hand, include both cross-sectional and longitudinal designs which link the instrument change to a meaningful external anchor [17]. In the longitudinal designs the concept of "minimal clinically important difference" (MCID) has been introduced in an effort to define what is the smallest meaningful change score [11,18,19]. These methods have advantages and limitations and many authors propose to use both approaches [17,19,20]. Apart from the type of responsiveness index, other factors affect the size of the responsiveness index such as type of intervention, patient population under study, and timing of data collection [17,21,22]. Therefore head-to-head comparisons of responsiveness in low back pain (LBP) specific instruments in different study settings and in different subpopulations of back pain patients are of paramount importance. A literature search revealed that headto-head comparisons has been made for 1) a general LBP population [23-30] 2), a general LBP population in relation to baseline entry scores [8,31-33], 3) specific subpopulations of back pain patients [34-36], 4) conditionspecific vs. generic/patient-specific questionnaires [3741], 5) different external criteria (anchors) [34,42], 6) http://www.biomedcentral.com/1471-2474/7/82 pain, disability and physical impairment indices [43], and lastly as part of an instrument validation study [44-55]. Thus, concurrent comparisons of responsiveness in subpopulations of LBP pa (...truncated)